An outbreak of chikungunya fever which occurred during April 1977 among a group of high-school children from Pretoria after a visit to the northern Transvaal bushveld is reported. Some of the adults who accompanied the pupils also contracted the disease. The adults suffered more severely from the chronic arthritic form of the disease than did the children. In some cases the episodic polyarthritis was still present 18 months after the onset of the disease. Rheumatoid factors in low titre could be demonstrated in the circulation of patients with longstanding symptoms.